McDonald et al correlated the ratio of C-peptide to creatinine in a spot urine specimen with the amount of C-peptide in a 24 hour urine. This can give insights into daily release of insulin. The authors are from Peninsula Medical School and the Royal Devon and Exeter NHS Foundation Trust in Exeter, UK.


Specimen: second void fasting urine


Advantages of testing a spot urine sample:

(1) easier and more convenient to collect compared to a 24 hour specimen

(2) plasma C-peptide is rapidly degraded due to proteases



(1) urine C-peptide in nmol/L

(2) urine creatinine in mmol/L


ratio of C-peptide to creatinine in urine =

= (urine C-peptide) / (urine creatinine)


According to Figure 2 (page 2038) a regression line can be drawn for a plot of the ratio vs 24 hour urine C-peptide in nmol/L.


24 hour urine C-peptide in nmol/L =

= (13.24 * (ratio of C-peptide to creatinine)) + 14.79


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